The book does not teach anything. It's largely an upsell to Sadhguru's cultish meditation programmes.
Meditation instructions in the book are something like: a) pay attention to your heartbeat, or your breath, or your little finger for 11 minutes three times a day, b) eat less food, mostly raw, c) draw mandalas on the floor and place a ghee lamp in it and notice how the energy of the room subtly changes. This is a joke, right? It reads like somebody who doesn't know anything about meditation is lampooning meditation.
Sadhguru himself is an aspiring cult leader who teaches pseudoscentific twaddle like drinking happy water (because he claims water carries emotional memory [1]), how he can trap evil spirits in boxes with obscure tantric rituals (like Ghostbusters), encountering the frozen spirits of Native American soldiers in a forest [2], etc. He also claims his wife died by attaining Mahasamadhi [3] (allegedly you can meditate really hard and make your soul leave your body). Regardless of the murder charge, having to believe this nonsense to get with his programme seems hardly worth it.
[1] https://www.youtube.com/watch?v=6C1p4HUHlfE
[2] https://www.youtube.com/watch?v=yBKvFnABpcA
[3] https://ksmphanindra.wordpress.com/2017/11/02/the-controvers...
https://www.youtube.com/embed/K4hCvdDn7Zc (important introduction)
https://www.youtube.com/embed/wHnl_XugJyE (instructions and guided meditation).
I practised this twice a day for about 2 months before completing the Inner Engineering program and it was a very good experience. I have now switched to Shambavi but that takes longer and comes with more strict practice conditions.
To give you a little background about myself, I'm a 27-year-old male software engineer. Before Isha I wasn't religious or spiritual, but I always thought some of the Eastern stuff (buddhism, taoism) I heard sounded interesting. I also had experiences with psychedelics that were very profound to me.
Anyway I found Sadhguru on YouTube one day and everything he was saying just really vibed with me. He's explaining millenia-old yogic ideas in modern terms, and it really resonated with my intellect as well as with my own personal experiences with psychedelics. They talk about nature in terms of space, time, and energy. They talk about the human mechanism and consciousness. They talk about yoga as a method of liberation or enlightenment, the end of suffering.
So then I started going to the programs and doing yoga. I've attended and volunteered at several programs. The people that go to these programs are all regular people like me. Maybe around two thirds are Indian, which makes sense because that's where yoga originated and where Sadhguru is from. I've met other engineers, physicians, professors, businessmen, etc. I would say that the common factor among all of us is that we each have a desire to have some deeper understanding of life, so we are willing to listen to Sadhguru and try out yoga.
It's been an awesome journey. Sadhguru and his foundation have had a huge effect on my life, and I'm very thankful for it.